Arduino code to control polarization rotator (switcher) based on USB commands.

polarization_rotator.pde

// polarization rotator experiment

int incomingByte = 1;	// for incoming serial data
int pwmPin = 9; // white wire
int dirPin = 11; // green wire
int statusLED = 13;
int delaymsec = 100;

void setup() {
  Serial.begin(9600);	// opens serial port, sets data rate to 9600 bps
  // initialize pwm and dir pins as outputs.
  pinMode(pwmPin, OUTPUT);
  pinMode(dirPin, OUTPUT);
  pinMode(statusLED, OUTPUT); // status LED
}

void loop() {
  // check for incoming serial data:
  if (Serial.available() > 0) {
    // read the incoming byte:
    incomingByte = int(Serial.read()) - 48;
  }
  if (incomingByte == 1) {
    //volage-state ON, polarization NOT rotated, status LED ON
    digitalWrite(statusLED,HIGH);
    digitalWrite(pwmPin, HIGH);
    analogWrite(dirPin, 127);
    delay(delaymsec);
  }
  if (incomingByte == 2) {
    //volage-state OFF, polarization IS rotated, status LED OFF
    digitalWrite(statusLED,LOW);
    digitalWrite(pwmPin, LOW);
    analogWrite(dirPin, LOW);
    delay(delaymsec);
  }
  incomingByte = 0; // no new data, skip all updates
}